西藏拉萨地块中—新生代火山岩中多硅白云母捕虏晶特征及其地质意义  

Phengite Xenocryst in Mesozoic-Cenozoic Volcanic Rocks from Lhasa Block and Its Geological Implications

作　　者：江万[1] 吴珍汉[1] 叶培盛[1] 胡道功[1] 

机构地区：[1]中国地质科学院地质力学研究所,北京100081

出　　处：《现代地质》2007年第2期286-290,共5页Geoscience

基　　金：国家重点基础研究发展规划项目(2002CB412600);科技部国际合作项目(2005DFA20680);中国地质调查局1:25万区域地质调查项目(200013000166)

摘　　要：在西藏班戈县德庆区纳木错西岸则弄群火山岩剖面中一段流纹质熔结凝灰岩岩石，西藏堆龙德庆县门堆乡帕那组火山岩剖面三段流纹质晶屑玻屑凝灰岩，以及西藏林周县强嘎乡帕那组火山岩剖面二段流纹质熔结凝灰岩中，发现了多硅白云母捕虏晶。多硅白云母捕虏晶的矿物成分分析结果显示其Si阳离子数为3．294—3．485，Al阳离子数为2．024—2．419，属于比较典型的高压／超高压岩石中常见的白云母。这一特征暗示早白垩世与始新世拉萨地块南北下地壳应该存在高压变质岩或发生过强烈构造挤压导致的高压变质作用。Some phengite xenocrysts were identified in early Cretaceous Zenong Group and Eocene Pana Formation volcanic rocks from Lhasa block. These white K-micas are generally subeuhedral to euhedral shape up to three millimeters large flakes with a reaction margin and are associated with sphene xenocryst, And they are not igneous minerals but xenocrysts. Electronic microprobe analysis suggests that contents of white K-micas vary from 3. 29 to 3.49 Si atoms per formula unit, and 2. 024 to 2. 419 Al atom per formula unit, which belongs to typical high-pressure/ultrahigh pressure phengite. This discovery hints distinctively about high-pressure metamorphism or crustal thickening occurred in northern Lhasa block in early Cretaceous and southern Lhasa block in Eocene.

关 键 词：多硅白云母 火山岩捕虏晶 拉萨地块 地壳增厚 

分 类 号：P588.1[天文地球—岩石学]